Method and apparatus for updating security key in wireless communication system

ABSTRACT

A communication technique and a system for fusing a 5th-generation (5G) or pre-5G communication system for supporting a higher data rate than that of a 4th-generation (4G) communication system, such as long-term evolution (LTE), with Internet of things (IoT) technology is provided. The communication technique includes an intelligent services (e.g., a smart home, a smart building, a smart city, a smart car or a connected car, healthcare, digital education, retail, security- and safety-related services, and the like), based on 5G communication technology and IoT-related technology. Moreover, a method and an apparatus for updating a security key in a wireless communication system are provided.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is based on and claims priority under 35 U.S.C. §119(e) of a U.S. provisional application Ser. No. 62/916,351, filed onOct. 17, 2019, in the U.S. Patent and Trademark Office, the disclosureof which is incorporated by reference herein in its entirety.

BACKGROUND 1. Field

The disclosure relates to a method and an apparatus for updating asecurity key in a wireless communication system. More specifically, thedisclosure relates to a method for, when a control message indicatinghandover includes several absolute radio frequency channel numbers(ARFCNs) and several physical cell identities (PCIs), selecting one PCIand one ARFCN to derive a new security key.

2. Description of the Related Art

To meet the demand for wireless data traffic having increased sincedeployment of fourth generation (4G) communication systems, efforts havebeen made to develop an improved fifth generation (5G) or pre-5Gcommunication system. Therefore, the 5G or pre-5G communication systemis also called a “Beyond 4G Network” or a “Post long term evolution(LTE) System”.

The 5G communication system is considered to be implemented in higherfrequency millimeter (mmWave) bands, e.g., 60 GHz bands, so as toaccomplish higher data rates. To decrease propagation loss of the radiowaves and increase the transmission distance, the beamforming, massivemultiple-input multiple-output (MIMO), full dimensional MIMO (FD-MIMO),array antenna, an analog beam forming, large scale antenna techniquesare discussed in 5G communication systems.

In addition, in 5G communication systems, development for system networkimprovement is under way based on advanced small cells, cloud radioaccess networks (RANs), ultra-dense networks, device-to-device (D2D)communication, wireless backhaul, moving network, cooperativecommunication, coordinated multi-points (CoMP), reception-endinterference cancellation and the like.

In the 5G system, hybrid frequency shift keying (FSK) and quadratureamplitude modulation (QAM) (FQAM) and sliding window superpositioncoding (SWSC) as an advanced coding modulation (ACM), and filter bankmulti carrier (FBMC), non-orthogonal multiple access (NOMA), and sparsecode multiple access (SCMA) as an advanced access technology have alsobeen developed.

For the 5G system, studies are being conducted to support a widervariety of services than the existing 4G system. For example, the mostrepresentative services of the 5G system include an enhanced mobilebroadband (eMBB) service, an ultra-reliable and low latencycommunication (URLLC) service, a massive machine type communication(mMTC) service, an evolved multimedia broadcast/multicast service(eMBMS), and the like. Further, a system for providing the URLLC servicemay be referred to as a URLLC system, and a system for providing theeMBB service may be referred to as an eMBB system. In addition, theterms “service” and “system” may be used interchangeably.

Among these services, the URLLC service is a service that is newlyconsidered in the 5G system, in contrast to the existing 4G system, andrequires to satisfy ultrahigh reliability (e.g., packet error rate ofabout 10-5) and low latency (e.g., about 0.5 msec) conditions comparedto the other services. In order to satisfy such strict requirements, theURLLC service may need to apply a transmission time interval (TTI) thatis shorter than that of the eMBB service, and various operating methodsusing this are under consideration.

The Internet, which is a human centered connectivity network wherehumans generate and consume information, is now evolving to the Internetof things (IoT) where distributed entities, such as things, exchange andprocess information without human intervention. The Internet ofeverything (IoE), which is a combination of the IoT technology and thebig data processing technology through connection with a cloud server,has emerged. As technology elements, such as “sensing technology”,“wired/wireless communication and network infrastructure”, “serviceinterface technology”, and “security technology” have been demanded forIoT implementation, a sensor network, a machine-to-machine (M2M)communication, machine type communication (MTC), and so forth have beenrecently researched.

Such an IoT environment may provide intelligent Internet technologyservices that create a new value to human life by collecting andanalyzing data generated among connected things. IoT may be applied to avariety of fields including smart home, smart building, smart city,smart car or connected cars, smart grid, health care, smart appliancesand advanced medical services through convergence and combinationbetween existing information technology (IT) and various industrialapplications.

In line with this, various attempts have been made to apply 5Gcommunication systems to IoT networks. For example, technologies such asa sensor network, machine type communication (MTC), andmachine-to-machine (M2M) communication may be implemented bybeamforming, MIMO, and array antennas. Application of a cloud radioaccess network (RAN) as the above-described big data processingtechnology may also be considered an example of convergence of the 5Gtechnology with the IoT technology.

The above information is presented as background information only toassist with an understanding of the disclosure. No determination hasbeen made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the disclosure.

SUMMARY

An embodiment proposes a method wherein, when a handover in whichseveral physical cell identities (PCIs) and several absolute radiofrequency channel numbers (ARFCNs) are involved is performed in awireless communication system, a terminal and a base station update asecurity key by using the same PCI and ARFCN.

The technical issues to be addressed in the disclosure are not limitedto the above described technical issues, and other technical issues thathave not been mentioned may be clearly understood by those skilled inthe art from the following description.

Aspects of the disclosure are to address at least the above-mentionedproblems and/or disadvantages and to provide at least the advantagesdescribed below. Accordingly, an aspect of the disclosure is to providean apparatus and a method for updating a security key in a wirelesscommunication system.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the presented embodiments.

In accordance with an aspect of the disclosure, a method performed by aterminal in a wireless communication system is provided. The methodincludes receiving, from a base station, a message including informationon at least one serving cell, determining whether the message includes afirst absolute radio frequency channel number (ARFCN) for a specificserving cell, and determining a first key for a master cell group basedon a first physical cell identity (PCI) for the specific serving celland the first ARFCN for the specific serving cell, in case that themessage includes the first ARFCN for the specific serving cell.

In an embodiment of the disclosure, the method further comprisesdetermining the first key for the master cell group based on the firstPCI for the specific serving cell and a second ARFCN used to determine acurrent first key for the master cell group, in case that the messagedoes not include the first ARFCN for the specific serving cell.

In an embodiment of the disclosure, the method further comprisesidentifying that the message includes information for indicating whetherthe first PCI and the first ARFCN is used to determine the first key,and determining the first key based on a current first key for themaster cell group, in case that the information indicates the first PCIand the first ARFCN is not used to determine the first key.

In an embodiment of the disclosure, the determining whether the messageincludes the first ARFCN for a specific serving cell comprises:determining whether the message includes the first ARFCN for a specificserving cell, in case that the information indicates the first PCI andthe first ARFCN is used to determine the first key.

In an embodiment of the disclosure, the information on the at least oneserving cell comprises the first PCI and two ARFCN for the specificserving cell.

In an embodiment of the disclosure, the first ARFCN among the two ARFCNindicates a center frequency of the specific serving cell and a secondARFCN indicates a lower end frequency of the specific serving cell.

In an embodiment of the disclosure, the specific serving cell is aprimary cell of the master cell group.

In an embodiment of the disclosure, the first ARFCN for the specificserving cell is listed in the message prior to an ARFCN for otherserving cell.

In accordance with another aspect of the disclosure, a terminal in awireless communication system is provided. The terminal includes atransceiver, and a controller configured to receive, from a base stationvia the transceiver, a message including information on at least oneserving cell, determine whether the message includes a first absoluteradio frequency channel number (ARFCN) for a specific serving cell, anddetermine a first key for a master cell group based on a first physicalcell identity (PCI) for the specific serving cell and the first ARFCNfor the specific serving cell, in case that the message includes thefirst ARFCN for the specific serving cell.

According to an embodiment of the disclosure, a terminal and a basestation update a security key by using the same PCI and ARFCN, so as toprevent breakdown of a service due to mismatch of the security key.

Other aspects, advantages, and salient features of the disclosure willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses various embodiments of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainembodiments of the disclosure will be more apparent from the followingdescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1A illustrates a structure of a new radio (NR) system according toan embodiment of the disclosure;

FIG. 1B illustrates a wireless protocol structure in long term evolution(LTE) and NR systems according to an embodiment of the disclosure;

FIG. 1C is a diagram illustrating carrier aggregation in a userequipment (UE) according to an embodiment of the disclosure;

FIG. 1D illustrates a procedure of a UE and a base station, related tokey updating at a time of a handover according to an embodiment of thedisclosure;

FIG. 1E is a diagram illustrating a UE operation performed at a time ofkey updating according to an embodiment of the disclosure;

FIG. 1F is a diagram depicting a UE operation for key updating in 1^(st)type reconfiguration according to an embodiment of the disclosure;

FIG. 1G is a diagram depicting a UE operation for key updating in 2^(nd)type reconfiguration according to an embodiment of the disclosure;

FIG. 1H is a diagram illustrating an order of UE operations performed ina case when a time alignment timer (TAT) of a primary secondary cell(PSCell) is expired while a configured secondary cell group (SCG) isinactive according to an embodiment of the disclosure;

FIG. 1I is a diagram illustrating a block configuration of a UEaccording to an embodiment of the disclosure; and

FIG. 1J is a diagram illustrating a block configuration of a basestation according to an embodiment of the disclosure.

The same reference numerals are used to represent the same elementsthroughout the drawings.

DETAILED DESCRIPTION

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of variousembodiments of the disclosure as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the various embodiments describedherein can be made without departing from the scope and spirit of thedisclosure. In addition, descriptions of well-known functions andconstructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but, are merely used by theinventor to enable a clear and consistent understanding of thedisclosure. Accordingly, it should be apparent to those skilled in theart that the following description of various embodiments of thedisclosure is provided for illustration purpose only and not for thepurpose of limiting the disclosure as defined by the appended claims andtheir equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

In the following description, terms for identifying access nodes, termsreferring to network entities, terms referring to messages, termsreferring to interfaces between network entities, terms referring tovarious identification information, and the like are illustratively usedfor the sake of convenience. Therefore, the disclosure is not limited bythe terms as used below, and other terms referring to subjects havingequivalent technical meanings may be used.

In the following description, the disclosure will be described usingterms and names defined in the LTE and NR standards, which are thelatest standards defined by the 3^(rd) generation partnership projectlong term evolution (3GPP LTE) group, for the convenience ofdescription. However, the disclosure is not limited by these terms andnames, and may be applied in the same way to systems that conform otherstandards. More particularly, the disclosure may be applied to the 3GPPNR (or 5^(th) generation/5G mobile communication standard).

FIG. 1A illustrates a structure of an NR system according to anembodiment of the disclosure.

Referring to FIG. 1A, a wireless communication system may be configuredby several base stations 1 a-05, 1 a-10, 1 a-15, and 1 a-20, an accessand mobility management function (AMF) 1 a-25, and a user plan function(UPF) 1 a-30. A user equipment (hereinafter, UE or terminal) 1 a-35 mayaccess an external network through the base stations 1 a-05, 1 a-10, 1a-15, and 1 a-20 and the UPF 1 a-30.

The base stations 1 a-05, 1 a-10, 1 a-15, and 1 a-20 serve as accessnodes of a cellular network, and provides a wireless access to UEsaccessing the network. For example, in order to service traffic ofusers, the base stations 1 a-05, 1 a-10, 1 a-15, and 1 a-20 collectstate information of UEs 1 a-35, such as a buffer state, an availabletransfer power state, and a channel state and perform scheduling, so asto support a connection between the UEs 1 a-35 and a core network (CN.More particularly, a CN of NR is referred to as a 5GC). Incommunications, a user plane (UP) related to transmission of real userdata and a control plane (CP) such as connection management may beseparately configured. In FIG. 1A, the gNBs 1 a-05 and 1 a-20 use UP andCP technology defined in NR technology, and although the ng-eNBs 1 a-10and 1 a-15 are connected to a 5GC, the ng-eNBs use UP and CP technologydefined in LTE technology.

The AMF/SMF 1 a-25 is a device configured to perform various controlfunctions as well as a mobility management function for a UE, and isconnected to multiple base stations. The UPF 1 a-30 is kind of a gatewaydevice providing data transmission.

FIG. 1B illustrates a wireless protocol structure in LTE and NR systemsaccording to an embodiment of the disclosure.

Referring to FIG. 1B, the wireless protocol of the LTE and NR systemsincludes packet data convergence protocols (PDCPs) 1 b-05 and 1 b-40,radio link controls (RLCs) 1 b-10 and 1 b-35, and medium access controls(MACs) 1 b-15 and 1 b-30, for a UE and an eNB/gNB, respectively. Each ofthe packet data convergence protocols (PDCPs) 1 b-05 and 1 b-40 isconfigured to perform an operation such as IP headercompression/reconstruction, and each of the radio link controls(hereinafter, referred to as RLCs) 1 b-10 and 1 b-35 reconfigures aprotocol data unit (PDCP PDU) to be a proper size. Each of the MACs 1b-15 and 1 b-30 is connected to several RLC layer devices configured ina single UE, and multiplexes RLC PDUs to a MAC PDU, and demultiplexes aMAC PDU to RLC PDUs. Each of physical layers (PHYs) 1 b-20 and 1 b-25performs channel coding and modulation on upper layer data to make thedata into an OFDM symbol and transmit the OFDM symbol through a wirelesschannel, or performs demodulation and channel decoding on an OFDM symbolreceived through a wireless channel, and then transfers the OFDM symbolto an upper layer. In addition, the physical layer also uses a hybridautomatic repeat request (ARQ) (HARQ) for additional error correction,and a receiver transmits information relating to whether a packettransmitted by a transmitter is received, the information size being onebit. The information is referred to as HARQ ACK/NACK information.Downlink HARQ ACK/NACK information for uplink data transmission istransmitted through a physical hybrid-ARQ indicator channel (PHICH) inLTE. In NR, whether retransmission is required, and whether to performnew transmission may be determined through scheduling information of acorresponding UE in a physical downlink control channel (PDCCH) which isa channel through which downlink/uplink resource allocation istransmitted. This is because NR employs asynchronous HARQ. Uplink HARQACK/NACK information for downlink data transmission may be transmittedthrough a physical uplink control channel (PUCCH) or a physical uplinkshared channel (PUSCH). In general, a PUCCH is transmitted in the uplinkin a PCell, which is described later. However, if there is a support bya UE, a base station may additionally transmit the PUCCH to the UE evenin an SCell, which is described later, and the SCell in this case iscalled a PUCCH SCell.

Although not illustrated in FIG. 1B, radio resource control (RRC) layersexist above the PDCP layers of the UE and the base station,respectively, and the RRC layers may exchange anaccess/measurement-related configuration control message for wirelessresource control.

Each of the PHY layers 1 b-20 and 1 b-25 may be configured by one ormultiple frequencies/carriers, and a technology in which one basestation configures multiple frequencies at once and then uses themultiple frequencies is called carrier aggregation (hereinafter,referred to as CA) technology. Method of using only one carrier forcommunication between a terminal (or user equipment or UE) and a basestation (an eNB in LTE, or a gNB in NR), CA technology additionally usesone or multiple secondary carriers as well as primary carrier, and thuscan remarkably increase traffics in proportion to the number of thesecondary carriers according to the related art. In LTE, a cell in abase station, using a main carrier, is called a PCell (primary cell),and a secondary carrier is called a SCell (secondary cell). A technologyextending the CA function described above to two base station is calleddual connectivity technology (hereinafter, referred to as DC). In the DCtechnology, a UE uses a master base station (a master E-UTRAN nodeB(MeNB) or a master node (MN)), and a secondary base station (a secondaryE-UTRAN nodeB (SeNB) or a secondary node (SN)) together while connectingto both of them, and cells belonging to the master base station arecalled a master cell group (hereinafter, referred to as an MCG), andcells belonging to the secondary base station are called a secondarycell group (hereinafter, referred to as an SCG). There is arepresentative cell in each cell group, and the representative cell ofthe master cell group is called a primary cell (a PCell or a SpCell(special cell) of the master cell group), and the representative cell ofthe secondary cell group is called a primary secondary cell (a PSCell ora primary SCG cell). If NR described above is used, the MCG is usedthrough LTE technology and the SCG is used through NR, so that a UE canuse both LTE and NR. In NR, there may be a maximum of 16 serving cells(a PCell or SCells in an MCG, and a PSCell and SCells in an SCG) in eachcell group (i.e., an MCG or SCG).

Although not illustrated in FIG. 1B, radio resource control (RRC) layersexist above the PDCP layers 1 b-05 and 1 b-40 of the UE and the basestation, respectively, and the RRC layers may exchange anaccess/measurement-related configuration control message for wirelessresource control. For example, measurement may be indicated to the UE byusing a message from the RRC layer, and the UE may report a result ofthe measurement to the base station by using a message from the RRClayer.

FIG. 1C is a diagram illustrating carrier aggregation technology in a UEaccording to an embodiment of the disclosure.

Referring to FIG. 1C, one base station 1 c-05 generally transmits andreceives multi-carriers over several frequency bands. For example, whenthe base station 1 c-05 transmits a carrier 1 c-15 having a centerfrequency of f1, and a carrier 1 c-10 having a center frequency of f3,one UE 1 c-30 transmits or receives data by using one carrier among thetwo carriers in the method of the related art. However, the UE 1 c-30having a carrier aggregation ability may transmit or receive data fromseveral carriers at the same time. The base station 1 c-05 may assignmore carriers to the UE 1 c-30 having the carrier aggregation abilityaccording to a situation, so as to increase the transmission speed ofthe UE 1 c-30.

If one forward-link carrier and one reverse-link carrier that aretransmitted and received by one base station 1 c-05 configure a singlecell, carrier aggregation may be also interpreted as transmitting orreceiving data through several cells at the same time by the UE 1 c-30of the related art. Therefore, the maximum transmission speed increasesproportionally with the number of aggregated carriers.

Hereinafter, in describing the disclosure, the fact that a UE receivesdata through a random forward-link carrier, or transmits data through arandom reverse-link carrier may imply the same meaning as the fact thatthe UE transmits or receives the data by using a control channel and adata channel provided in a cell corresponding to the center frequencyand the frequency band characterizing the carrier. In addition, forconvenience of explanation, embodiments below will be explained under anassumption of an LTE system, but the disclosure may be applied tovarious types of wireless communication systems supporting carrieraggregation.

Security is one of most important feature that mobile communicationshould provide. To achieve the required level of security,ciphering/deciphering and integrity protection are applied to the datapackets exchanged in the air interface. Security function is performedin the PDCP layer, hence those operations likeciphering/deciphering/integrity protection are applied to PDCP SDUs(service data units).

A security key is required to be generated by using various inputs sothat a third party is unable to derive the security key. For example,the inputs may be frequency information (an ARFCN), a PCI, and the like.A base station indicates updating of a master key by transmitting apredetermined control message to a UE. If the control message includesonly one PCI and one piece of frequency information, the UE and the basestation update the master key by using identical inputs. For reference,the master key has a concept in contrast to that of a secondary key, andmeans a security key applied in a master cell group of the UE.

It may be efficient to include several PCIs and several pieces offrequency information in one control message. For example, if the basestation configures carrier aggregation while indicating updating of akey through a single control message, the control message may include asmany PCIs as newly configured serving cells and as many pieces offrequency indicators as the newly configured serving cells. In addition,it may be efficient to include multiple pieces of frequency informationin one serving cell. For example, it may be required that both frequencyinformation indicating the center frequency of a cell and frequencyinformation indicating the boundary frequency of the cell are included.The frequency information is indicated by an absolute radio frequencychannel number (ARFCN).

The disclosure provides a method and an apparatus for using, for keyupdating, a predetermined PCI and a predetermined piece of frequencyinformation among multiple PCIs and multiple pieces of frequencyinformation, so as to indicate key updating through a control messageincluding the multiple PCIs and the multiple pieces of frequencyinformation. More specifically, a UE applies, to key updating, a PCIsatisfying a predetermined condition among multiple PCIs, and applies,to key updating, a piece of frequency information satisfying apredetermined condition among multiple pieces of frequency information.

FIG. 1D illustrates a procedure of a UE and a base station, related tokey updating at a time of a handover according to an embodiment of thedisclosure.

Referring to FIG. 1D, a UE 1 d-01 reports a measurement report includinga measurement result to a base station 1 d-03 in operation 1 d-11. Byreferring to the message including information such as the wirelessquality of a neighboring cell, the base station 1 d-03 may perform thefollowing operations related to determination on whether to perform ahandover in operation 1 d-21.

Determination on whether to perform a handover: For example, if thewireless channel quality of the neighboring cell is better than thewireless channel quality of the current cell, the base station 1 d-03may determine to perform a handover of a target cell to the neighboringcell.

Determination on a type of the handover: The base station 1 d-03 maydetermine the type of the handover by considering a performance of theUE 1 d-01, a traffic type, and a load of a cell.

Determination on PCIs and ARFCNs to be included in a RRCReconfigurationmessage After the handover, the base station 1 d-03 may determine PCIsand ARFCNs to be included, by considering whether carrier aggregation isapplied.

Determination on whether to perform key updating, and a type of the keyupdating: The base station 1 d-03 may determine whether to perform keyupdating by considering a base station controlling the target cell.

Determination on a PCI and an ARFCN to be applied to key updating: Thebase station 1 d-03 may determine whether to perform key updating byconsidering a frequency of the target cell.

Determination on a position where a PCI and an ARFCN for key updatingare stored: The base station 1 d-03 stores a PCI to be used for keyupdating as the foremost PCI among PCIs to be included in the RRCReconfiguration message. The base station 1 d-03 may store an ARFCN tobe used for key updating as the foremost ARFCN among ARFCNs to beincluded in the RRC reconfiguration message.

The base station 1 d-03 may transmit an RRC reconfiguration messageindicating a handover to the UE 1 d-01 in operation 1 d-31. The RRCreconfiguration message may include several PCIs and several ARFCNs, andmay include information specifying a type of the handover.

The UE 1 d-01 may start an RRC reconfiguration procedure related to thehandover at a proper time point according to the type of the indicatedhandover in operation 1 d-41. If the type is the 1^(st) type or the2^(nd) type, the UE 1 d-01 may start a handover procedure immediatelywhen the RRC reconfiguration message indicating the handover isreceived. If the type is the 3^(rd) type, the UE 1 d-01 may start ahandover procedure when a predetermined condition is satisfied after theRRC reconfiguration message indicating the handover is received.

The UE 1 d-01 performs key updating in operation 1 d-51. Key updating ofthe UE 1 d-01 and key updating of the base station 1 d-03 may beperformed at different time points. A key updating procedure includesthe stages: deriving a new key and applying the new key. The UE 1 d-01may perform key updating at the time point of the handover, and the basestation 1 d-03 may derive a new key in operation 1 d-11 and apply thenew key when the handover starts.

When the UE 1 d-01 derives a key, the UE may select a PCI and an ARFCNdetermined according to a predetermined rule according to the type ofthe handover, and input the selected PCI and ARFCN to a key derivationfunction.

The UE 1 d-01 and the base station 1 d-03 may apply the new key toperform data transmission/reception in operation 1 d-61.

FIG. 1E is a diagram illustrating a UE operation performed at a time ofkey updating according to an embodiment of the disclosure.

Referring to FIG. 1E, the UE receives RRCReconfiguration messagecontaining reconfigurationWithSync from a base station in operation 1e-01.

The UE determines the type of reconfiguration in operation 1 e-02. TheUE determines the type of reconfiguration based on the presence ofspecific indication in the reconfiguration message. If first information(i.e., reconfigurationWithSync type 2 indicator) is included, it is thesecond type reconfiguration. If second information (conditionalreconfigurationWithSync related information) is included, it is thethird type reconfiguration. If none of above but onlyreconfigurationWithSync is included, it is the first typereconfiguration.

If it is first type reconfiguration, the UE performs the key update forthe first type reconfiguration in operation 1 e-03.

If it is second type reconfiguration, the UE performs the key update forthe second type reconfiguration in operation 1 e-04.

If it is third type reconfiguration, the UE performs the key update forthe third type reconfiguration in operation 1 e-05.

RRCReconfiguration message can include the following information.

RRCReconfiguration-v 1530-IEs ::= SEQUENCE { masterCellGroup OCTETSTRING (CONTAINING CellGroupConfig) OPTIONAL, -- Need M fullConfigENUMERATED {true} OPTIONAL, -- Cond FullConfig dedicatedNAS-MessageListSEQUENCE (SIZE(1..maxDRB)) OF DedicatedNAS-Message OPTIONAL, -- CondnonHO masterKeyUpdate  MasterKeyUpdate OPTIONAL, -- Cond MasterKeyChangededicatedSIB1-Delivery OCTET STRING (CONTAINING SIB1) OPTIONAL, -- NeedN dedicatedSystemInformationDelivery OCTET STRING (CONTAININGSystemInformation) OPTIONAL, -- Need N otherConfig OtherConfig OPTIONAL,-- Need M nonCriticalExtension  RRCReconfiguration-v1540-IEs OPTIONAL }RRCReconfiguration-v1610-IEs ::= SEQUENCE { otherConfig-v1610 OtherConfig-v1610 OPTIONAL, -- Need M bap-Config-r16 SetupRelease {BAP-Config-r16 } OPTIONAL, -- Need M iab-IP-AddressConfigurationList-r16IAB-IP-AddressConfigurationList-r16 OPTIONAL, -- Need MconditionalReconfiguration-r16 ConditionalReconfiguration-r16 OPTIONAL,-- Need M daps-SourceRelease-r16 ENUMERATED{true} OPTIONAL, -- Need Nt316-r16 SetupRelease {T316-r16} OPTIONAL, -- Need MneedForGapsConfigNR-r16 SetupRelease {NeedForGapsConfigNR-r16} OPTIONAL,-- Need M onDemandSIB-Request-r16 SetupRelease { OnDemandSIB-Request-r16} OPTIONAL, -- Need M dedicatedPosSysInfoDelivery-r16  OCTET STRING(CONTAINING PosSystemInformation-r16-IEs) OPTIONAL, -- Need Nsl-ConfigDedicatedNR-r16 SetupRelease {SL-ConfigDedicatedNR-r16}OPTIONAL, -- Need M sl-ConfigDedicatedEUTRA-Info-r16 SetupRelease {SL-ConfigDedicatedEUTRA-Info-r16} OPTIONAL, -- Need M nonCriticalExtensionSEQUENCE {} OPTIONAL }

reconfigurationWithSync type 2 indicator is daps-Config inRadioBearerConfig. second information is conditionalReconfiguration.

MasterKeyUpdate can include the following information.

MasterKeyUpdate ::= SEQUENCE { keySetChangeIndicator  BOOLEAN,nextHopChainingCount NextHopChainingCount, nas-Container OCTET STRINGOPTIONAL, -- Cond securityNASC ... }

CellGroupConfig and ServingCellConfigCommon can include the followinginformation

-- ASN1START -- TAG-CELLGROUPCONFIG-START -- Configuration of oneCell-Group: CellGroupConfig ::= SEQUENCE { cellGroupId CellGroupId,rlc-BearerToAddModList SEQUENCE (SIZE(1..maxLC-ID)) OF RLC-BearerConfigOPTIONAL, -- Need N rlc-BearerToReleaseList SEQUENCE (SIZE(1..maxLC-ID))OF LogicalChannelIdentity OPTIONAL, -- Need N mac-CellGroupConfig MAC-CellGroupConfig OPTIONAL, -- Need M physicalCellGroupConfigPhysicalCellGroupConfig OPTIONAL, -- Need M spCellConfig SpCellConfigOPTIONAL, -- Need M sCellToAddModList SEQUENCE(SIZE (1..maxNrofSCells))OF SCellConfig OPTIONAL, -- Need N sCellToReleaseList SEQUENCE (SIZE(1..maxNrofSCells)) OF SCellIndex OPTIONAL, -- Need N ..., [[reportUplinkTxDirectCurrent ENUMERATED {true} OPTIONAL -- CondBWP-Reconfig ]], [[ bap-Address-r16 BIT STRING (SIZE (10)) OPTIONAL, --Need M bh-RLC-ChannelToAddModList-r16 SEQUENCE (SIZE(1..maxBH-RLC-ChannelID-r16)) OF BH-RLC-ChannelConfig-r16 OPTIONAL, -- Need Nbh-RLC-ChannelToReleaseList-r16 SEQUENCE (SIZE(1..maxBH-RLC-ChannelID-r16)) OF BH-RLC-ChannelID-r16 OPTIONAL, -- Need Nf1c-TransferPath-r16  ENUMERATED {lte, nr, both} OPTIONAL, -- Need MsimultaneousTCI-UpdateListl-r16 SEQUENCE (SIZE(1..maxNrofServingCellsTCI-r16)) OF ServCellIndex OPTIONAL, -- Need RsimultaneousTCI-UpdateList2-r16 SEQUENCE (SIZE(1..maxNrofServingCellsTCI-r16)) OF ServCellIndex OPTIONAL, -- Need RsimultaneousSpatial-UpdatedList1-r16 SEQUENCE (SIZE(1..maxNrofServingCellsTCI-r16)) OF ServCellIndex OPTIONAL, -- Need RsimultaneousSpatial-UpdatedList2-r16 SEQUENCE (SIZE(1..maxNrofServingCellsTCI-r16)) OF ServCellIndex OPTIONAL, -- Need RuplinkTxSwitchingOption-r16 ENUMERATED {switchedUL, dualUL} OPTIONAL --Need R ]] } -- Serving cell specific MAC and PHY parameters for aSpCell: SpCellConfig ::= SEQUENCE { servCellIndex ServCellIndexOPTIONAL, -- Cond SCG reconfigurationWithSync ReconfigurationWithSyncOPTIONAL, -- Cond ReconfWithSync rlf-TimersAndConstants SetupRelease {RLF-TimersAndConstants } OPTIONAL, -- Need M rlmInSyncOutOfSyncThresholdENUMERATED {n1} OPTIONAL, -- Need S spCellConfigDedicatedServingCellConfig OPTIONAL, -- Need M ... } ReconfigurationWithSync ::=SEQUENCE { spCellConfigCommon  ServingCellConfigCommon OPTIONAL, -- NeedM newUE-Identity RNTI-Value, t304 ENUMERATED {ms50, ms100, ms150, ms200,ms500, ms1000, ms2000, ms10000}, rach-ConfigDedicated CHOICE { uplinkRACH-ConfigDedicated, supplementaryUplink RACH-ConfigDedicated }OPTIONAL, --Need N ..., [[ smtc SSB-MTC OPTIONAL -- Need S ]], [[daps-UplinkPowerConfig-r16 DAPS-UplinkPowerConfig-r16 OPTIONAL -- Need N]] } DAPS-UplinkPowerConfig-r16 ::= SEQUENCE { p-DAPS-Source-rl6  P-Max,p-DAPS-Target-r16 P-Max, uplinkPowerSharingDAPS-Mode-r16 ENUMERATED{semi-static-mode1, semi-static-mode2, dynamic } } SCellConfig ::=SEQUENCE { sCellIndex  SCellIndex, sCellConfigCommonServingCellConfigCommon OPTIONAL, -- Cond SCellAdd sCellConfigDedicatedServingCellConfig OPTIONAL, -- Cond SCellAddMod ..., [[ smtc SSB-MTCOPTIONAL -- Need S ]], [[ sCellState-r16 ENUMERATED {activated}OPTIONAL, -- Cond SCellAddSync secondaryDRX-GroupConfig-r16 ENUMERATED{true} OPTIONAL -- Cond DRX-Config2 ]]} -- TAG-CELLGROUPCONFIG-STOP --ASN1STOP ServingCellConfigCommon ::= SEQUENCE { physCellId PhysCellIdOPTIONAL, -- Cond HOAndServCellAdd, downlinkConfigCommonDownlinkConfigCommon OPTIONAL, -- Cond HOAndServCellAdduplinkConfigCommon UplinkConfigCommon OPTIONAL, -- Need MsupplementaryUplinkConfig UplinkConfigCommon OPTIONAL, -- Need Sn-TimingAdvanceOffset ENUMERATED { n0, n25600, n39936 } OPTIONAL, --Need S ssb-PositionsInBurst CHOICE { shortBitmap BIT STRING (SIZE (4)),mediumBitmap BIT STRING (SIZE (8)), longBitmap BIT STRING (SIZE (64)) }OPTIONAL, -- Cond AbsFreqSSB ssb-periodicityServingCell ENUMERATED {ms5, ms10, ms20, ms40, ms80, ms160, spare2, spare1 } OPTIONAL, -- Need Sdmrs-TypeA-Position ENUMERATED {pos2, pos3}, lte-CRS-ToMatchAround SetupRelease { RateMatchPatternLTE-CRS } OPTIONAL, -- Need MrateMatchPatternToAddModList SEQUENCE (SIZE(1..maxNrofRateMatchPatterns)) OF RateMatchPatternId OPTIONAL, -- Need NrateMatchPatternToReleaseList  SEQUENCE (SIZE(1..maxNrofRateMatchPatterns)) OF RateMatchPatternId OPTIONAL, -- Need NssbSubcarrierSpacing SubcarrierSpacing OPTIONAL, -- CondHOAndServCellWithSSB tdd-UL-DL-ConfigurationCommonTDD-UL-DL-ConfigCommon OPTIONAL, -- Cond TDD ss-PBCH-BlockPower INTEGER(−60..50), ..., [[ channelAccessMode-r16 CHOICE { dynamic NULL,semiStatic SemiStaticChannelAccessConfig } OPTIONAL, -- CondSharedSpectrum discoveryBurstWindowLength-r16 ENUMERATED {ms0dot5, ms1,ms2, ms3, ms4, ms5} OPTIONAL, -- Need M ssb-PositionQCL-r16SSB-PositionQCL-Relation-r16 OPTIONAL, -- Cond SharedSpectrumhighSpeedConfig-r16  HighSpeedConfig-r16 OPTIONAL -- Need R ]] } --TAG-SERVINGCELLCONFIGCOMMON-STOP -- ASN1STOP

FIG. 1F is a diagram depicting a UE operation for key updating in 1^(st)type reconfiguration according to an embodiment of the disclosure.

Referring to FIG. 1F, the UE determines whether RRCReconfigurationmessage includes the first information set (masterKeyUpdate) related tokey update for the master cell group operation 1 f-01.

If the RRCReconfiguration message does not include the first informationset, the UE ends the key update procedure without key update operation 1f-02.

If the RRCReconfiguration includes the first information set, the UEgoes to operation 1 f-03 to start key update procedure

The UE determines whether the first indicator (keyChangeIndicator) inthe first information set is set to true operation 1 f-03.

If it is set to true, the UE derives the first key for the master cellgroup without considering PCI and ARFCN operation 1 f-04. Morespecifically, the first key for the master cell group is derived fromthe current first key using a specific KDF (Key Derivation Function).

If the first indicator in the first information set is set to false, theUE derives the first key for the master cell group based on a first PCIand a first ARFCN among multiple PCIs and multiple ARFCNs contained inthe message operation 1 f-05. The first PCI is the PCI included in the1st IE of the RRCReconfiguration message. RRCReconfiguration message caninclude multiple PCIs. A PCI can be included in the 1st IE, 2nd IE, 3rdIE or 4th IE. The 1st IE is spCellConfigCommon inreconfigurationWithSync in spCellConfig in cellGroupConfig formasterCellGroup. The 1^(st) IE is the set of information on the primarycell of master cell group after handover. The 2nd IE issCellConfigCommon in sCellToAddModList in CellGroupConfig formasterCellGroup. The 2^(nd) IE is the set of information on thesecondary cells to be used after handover. The 3rd IE isspCellConfigCommon in reconfigurationWithSync in spCellConfig incellGroupConfig for mrdc-SecondaryCellGroupConfig. The 3^(rd) IE is setof information on the primary cell of secondary cell group. The 4th IEis sCellConfigCommon in sCellToAddModList in CellGroupConfig formrdc-SecondaryCellGroupConfig. The 4^(th) IE is set of information onthe secondary cells of secondary cell group. The first ARFCN is thefirst ARFCN indicated in the 5th IE (FrequencyInfoDL withinspCellConfigCommon within reconfigurationWithSync within spCellConfigwithin CellGroupConfig for master cell group) of the RRCReconfigurationmessage if the 5th IE is included in the RRCReconfiguration message. ARRCReconfiguration message can include multiple ARFCNs as followings.Two ARFCNs can be included in 5th IE, 6th IE, 7th IE and 8th IE. Thefirst ARFCN indicates the center frequency of a cell (or centerfrequency of reference signal representing the cell). The second ARFCNindicates the lower end frequency of a cell. The 5th IE isFrequencyInfoDL in spCellConfigCommon in reconfigurationWithSync inspCellConfig in cellGroupConfig for masterCellGroup. The 5^(th) IE issubset of 1^(st) IE and includes frequency relation information for aspecific cell corresponding to 1^(st) IE. The 6th IE is FrequencyInfoDLin sCellConfigCommon in sCellToAddModList in CellGroupConfig formasterCellGroup. The 6^(th) IE is subset of 2^(nd) IE and includesfrequency relation information for a specific cell corresponding to2^(nd) IE. The 7th IE is FrequencyInfoDL in spCellConfigCommon inreconfigurationWithSync in spCellConfig in cellGroupConfig formrdc-SecondaryCellGroupConfig. The 7^(th) IE is subset of 3^(rd) IE andincludes frequency relation information for a specific cellcorresponding to 3^(rd) IE. The 8th IE is FrequencyInfoDL insCellConfigCommon in sCellToAddModList in CellGroupConfig formrdc-SecondaryCellGroupConfig. The 8^(th) IE is subset of 4^(th) IE andincludes frequency relation information for a specific cellcorresponding to 4^(th) IE. The first ARFCN is the ARFCN having used toderive the current first key for the master cell group if the 5th IE isnot included in the RRCReconfiguration message

The UE derives the 2nd key (K_(RRC-enc)), 3rd key (K_(UP-enc)), 4th key(K_(RRC-int)) and 5th key (K_(UP-int)) from the 1st key (K_(gNB))according to key derivation function operation 1 f-06.

The UE applies the 2nd key and 3rd key to cipher and decipher the PDCPSDUs transmitted to and received from the target cell operation 1 f-07.

The UE applies the 4th key and 5th key for integrity protection for thePDCP SDUs transmitted to and received from the target cell operation 1f-08.

FIG. 1G is a diagram depicting a UE operation for key updating in 2^(nd)type reconfiguration according to an embodiment of the disclosure.

Referring to FIG. 1G, the UE determines whether RRCReconfigurationmessage includes the first information set (masterKeyUpdate) related tokey update for the master cell group operation 1 g-01.

If the RRCReconfiguration message does not include the first informationset, the UE ends the key update procedure without key update operation 1g-02.

If the RRCReconfiguration message includes the first information set,the UE goes to 1 g-05 to start key update procedure.

The UE derives the first key for the master cell group based on a firstPCI and a first ARFCN among multiple PCIs and multiple ARFCNs containedin the message operation 1 g-05. The first PCI is the PCI included inthe 1st IE of the RRCReconfiguration message. RRCReconfiguration messagecan include multiple PCIs. A PCI can be included in the 1st IE, 2nd IE,3rd IE or 4th IE. The 1st IE is spCellConfigCommon inreconfigurationWithSync in spCellConfig in cellGroupConfig formasterCellGroup. The 1^(st) IE is the set of information on the primarycell of master cell group after handover. The 2nd IE issCellConfigCommon in sCellToAddModList in CellGroupConfig formasterCellGroup. The 2^(nd) IE is the set of information on thesecondary cells to be used after handover. The 3rd IE isspCellConfigCommon in reconfigurationWithSync in spCellConfig incellGroupConfig for mrdc-SecondaryCellGroupConfig. The 3^(rd) IE is setof information on the primary cell of secondary cell group. The 4th IEis sCellConfigCommon in sCellToAddModList in CellGroupConfig formrdc-SecondaryCellGroupConfig. The 4^(th) IE is set of information onthe secondary cells of secondary cell group. The first ARFCN is thefirst ARFCN indicated in the 5th IE (FrequencyInfoDL withinspCellConfigCommon within reconfigurationWithSync within spCellConfigwithin CellGroupConfig for master cell group) of the RRCReconfigurationmessage if the 5th IE is included in the RRCReconfiguration message. ARRCReconfiguration message can include multiple ARFCNs as followings.Two ARFCNs can be included in 5th IE, 6th IE, 7th IE and 8th IE. Thefirst ARFCN indicates the center frequency of a cell (or referencesignal representing the cell). The second ARFCN indicates the lower endfrequency of a cell. The 5th IE is FrequencyInfoDL in spCellConfigCommonin reconfigurationWithSync in spCellConfig in cellGroupConfig formasterCellGroup. The 5^(th) IE is subset of 1^(st) IE and includesfrequency relation information for a specific cell corresponding to1^(st) IE. The 6th IE is FrequencyInfoDL in sCellConfigCommon insCellToAddModList in CellGroupConfig for masterCellGroup. The 6^(th) IEis subset of 2^(nd) IE and includes frequency relation information for aspecific cell corresponding to 2^(nd) IE. The 7th IE is FrequencyInfoDLin spCellConfigCommon in reconfigurationWithSync in spCellConfig incellGroupConfig for mrdc-SecondaryCellGroupConfig. The 7^(th) IE issubset of 3^(rd) IE and includes frequency relation information for aspecific cell corresponding to 3^(rd) IE. The 8th IE is FrequencyInfoDLin sCellConfigCommon in sCellToAddModList in CellGroupConfig formrdc-SecondaryCellGroupConfig. The 8^(th) IE is subset of 4^(th) IE andincludes frequency relation information for a specific cellcorresponding to 4^(th) IE. The first ARFCN is the ARFCN having used toderive the current first key for the master cell group if the 5th IE isnot included in the RRCReconfiguration message

The UE derives the 2nd key (K_(RRC-enc)), 3rd key (K_(UP-enc)), 4th key(K_(RRC-int)) and 5th key (K_(UP-int)) from the 1st key (K_(gNB))according to key derivation function operation 1 g-06.

The UE applies the new 2nd key and new 3rd key to cipher the PDCP SDUsafter random access in the target cell is successfully completed andapplies the current 2nd key and current 3rd key to cipher the PDCP SDUsbefore random access in the target cell is successfully completedoperation 1 g-07.

The UE applies the new 4th key, new 5th key, current 4th key and current5th key for integrity protection for the PDCP SDUs operation 1 g-08. Newkeys are applied to the PDCP SDUs transmitted to and received from thetarget cell. Current keys are applied to the PDCP SDUs transmitted toand received from the source cell.

FIG. 1H is a diagram illustrating an order of UE operations performed ina case when a time alignment timer (TAT) of a primary secondary cell(PSCell) is expired while a configured secondary cell group (SCG) isinactive according to an embodiment of the disclosure.

Referring to FIG. 1H, the UE evaluate whether a specific cell fulfillsthe condition for reconfigurationWithSync (i.e., certain conditionrelated with a specific measurement identity is fulfilled or conditionalreconfiguration should be executed) operation 1 h-00. If a cell fulfillsthe condition, the UE goes to 1 h-01. The specific cell is the cell ofwhich configuration information is included in the RRCReconfigurationmessage. The condition is about the radio quality of the cell, andconfiguration information included in the RRCReconfiguration message isconditionally executed when the associated condition is met. Forconditional reconfiguration, an outer RRCReconfiguration message caninclude multiple inner RRCReconfiguration. Each of innerRRCReconfiguration message is relevant to (or associated with) a cell.The UE determines whether one of inner RRCReconfiguration messageassociated with the specific cell fulfilling the condition includes thefirst information set (masterKeyUpdate) related to key update for theMaster cell group operation 1 h-01.

If the RRCReconfiguration message does not include the first informationset, the UE ends the key update procedure without key update operation 1h-02.

If the RRCact includes the first information set, the UE goes tooperation 1 h-03 to start key update procedure.

The UE determines whether the first indicator (keyChangeIndicator) inthe first information set is set to true operation 1 h-03.

If it is set to true, the UE derives the first key for the master cellgroup without considering PCI and ARFCN operation 1 h-04. The first keyfor the master cell group is derived from the current first key using aspecific KDF (Key Derivation Function).

If the first indicator in the first information set is set to false, theUE derives the first key for the master cell group based on a first PCIand a first ARFCN among multiple PCIs and multiple ARFCNs contained inthe inner RRC message operation 1 h-05. The first PCI is the PCIincluded in the 1st IE of the RRCReconfiguration message.RRCReconfiguration message can include multiple PCIs. A PCI can beincluded in the 1st IE, 2nd IE, 3rd IE or 4th IE. The 1st IE isspCellConfigCommon in reconfigurationWithSync in spCellConfig incellGroupConfig for masterCellGroup. The 1^(st) IE is the set ofinformation on the primary cell of master cell group after handover. The2nd IE is sCellConfigCommon in sCellToAddModList in CellGroupConfig formasterCellGroup. The 2^(nd) IE is the set of information on thesecondary cells to be used after handover. The 3rd IE isspCellConfigCommon in reconfigurationWithSync in spCellConfig incellGroupConfig for mrdc-SecondaryCellGroupConfig. The 3^(rd) IE is setof information on the primary cell of secondary cell group. The 4th IEis sCellConfigCommon in sCellToAddModList in CellGroupConfig formrdc-SecondaryCellGroupConfig. The 4^(th) IE is set of information onthe secondary cells of secondary cell group. The first ARFCN is thefirst ARFCN indicated in the 5th IE (FrequencyInfoDL withinspCellConfigCommon within reconfigurationWithSync within spCellConfigwithin CellGroupConfig for master cell group) of the RRCReconfigurationmessage if the 5th IE is included in the RRCReconfiguration message. ARRCReconfiguration message can include multiple ARFCNs as followings.Two ARFCNs can be included in 5th IE, 6th IE, 7th IE and 8th IE. Thefirst ARFCN indicates the center frequency of a cell (or referencesignal representing the cell). The second ARFCN indicates the lower endfrequency of a cell. The 5th IE is FrequencyInfoDL in spCellConfigCommonin reconfigurationWithSync in spCellConfig in cellGroupConfig formasterCellGroup. The 5^(th) IE is subset of 1^(st) IE and includesfrequency relation information for a specific cell corresponding to1^(st) IE. The 6th IE is FrequencyInfoDL in sCellConfigCommon insCellToAddModList in CellGroupConfig for masterCellGroup. The 6^(th) IEis subset of 2^(nd) IE and includes frequency relation information for aspecific cell corresponding to 2^(nd) IE. The 7th IE is FrequencyInfoDLin spCellConfigCommon in reconfigurationWithSync in spCellConfig incellGroupConfig for mrdc-SecondaryCellGroupConfig. The 7^(th) IE issubset of 3^(rd) IE and includes frequency relation information for aspecific cell corresponding to 3^(rd) IE. The 8th IE is FrequencyInfoDLin sCellConfigCommon in sCellToAddModList in CellGroupConfig formrdc-SecondaryCellGroupConfig. The 8^(th) IE is subset of 4^(th) IE andincludes frequency relation information for a specific cellcorresponding to 4^(th) IE. The first ARFCN is the ARFCN having used toderive the current first key for the master cell group if the 5th IE isnot included in the RRCReconfiguration message

The UE derives the 2nd key (K_(RRC-enc)), 3rd key (K_(UP-enc)), 4th key(K_(RRC-int)) and 5th key (K_(UP-int)) from the 1st key (K_(gNB))according to key derivation function operation 1 h-06.

The UE applies the 2nd key and 3rd key to cipher and decipher the PDCPSDUs transmitted to and received from the target cell operation 1 h-07.

The UE applies the 4th key and 5th key for integrity protection for thePDCP SDUs transmitted to and received from the target cell operation 1h-08.

FIG. 1I is a diagram illustrating a block configuration of a UEaccording to an embodiment of the disclosure.

Referring to FIG. 1I, the UE may include a radio frequency (RF)processor 1 i-10, a baseband processor 1 i-20, a storage unit 1 i-30,and a controller 1 i-40.

The RF processor 1 i-10 performs a function, such as signal band change,amplification, and the like, for transmitting or receiving a signalthrough a wireless channel. For example, the RF processor 1 i-10 mayupconvert a baseband signal provided from the baseband processor 1 i-20,into an RF band signal, and then transmit the RF band signal through anantenna, and may downconvert an RF band signal received through theantenna, into a baseband signal. For example, the RF processor 1 i-10may include a transmission filter, a reception filter, an amplifier, amixer, an oscillator, a digital-to-analog converter (DAC), ananalog-to-digital converter (ADC), and the like. In FIG. 1I, only oneantenna is illustrated, but the UE may include a plurality of antennas.In addition, the RF processor 1 i-10 may include a plurality of RFchains. Moreover, the RF processor 1 i-10 may perform beamforming. Toperform the beamforming, the RF processor 1 i-10 may adjust the phaseand size of each of signals transmitted or received through a pluralityof antennas or antenna elements.

The baseband processor 1 i-20 performs a function of conversion betweena baseband signal and a bit stream according to a physical layerprotocol of a system. For example, when data is transmitted, thebaseband processor 1 i-20 generates complex symbols by encoding andmodulating a transmission bit stream. In addition, when data isreceived, the baseband processor 1 i-20 reconstructs a reception bitstream by demodulating and decoding a baseband signal provided from theRF processor 1 i-10. For example, in a case where an orthogonalfrequency division multiplexing (OFDM) scheme is applied, when data istransmitted, the baseband processor 1 i-20 generates complex symbols byencoding and modulating a transmission bit stream, maps the complexsymbols to subcarriers, and then configures OFDM symbols through inversefast Fourier transform (IFFT) calculation and cyclic prefix (CP)insertion. In addition, when data is received, the baseband processor 1i-20 divides a baseband signal provided from the RF processor 1 i-10, bythe units of OFDM symbols, reconstructs signals mapped to subcarriers,through fast Fourier transform (FFT) calculation, and then reconstructsa reception bit stream through demodulation and decoding.

The baseband processor 1 i-20 and the RF processor 1 i-10 transmit andreceive a signal as described above. Accordingly, the baseband processor1 i-20 and the RF processor 1 i-10 may be called a transmitter, areceiver, a transceiver, or a communication unit. In addition, at leastone of the baseband processor 1 i-20 and the RF processor 1 i-10 mayinclude different communication modules to process signals in differentfrequency bands. The different frequency bands may include a super highfrequency (SHF) (e.g., 2.5 GHz and 5 GHz) band, a millimeter (mm) wave(e.g., 60 GHz) band, and the like.

The storage unit 1 i-30 stores data such as a basic program, anapplication program, and configuration information for an operation ofthe UE.

The controller 1 i-40 controls overall operations of the UE. Forexample, the controller 1 i-40 transmits or receives a signal throughthe baseband processor 1 i-20 and the RF processor 1 i-10. In addition,the controller 1 i-40 records and reads data in and from the storageunit 1 i-30. To this end, the controller 1 i-40 may include at least oneprocessor. For example, the controller 1 i-40 may include acommunication processor (CP) performing a control for communication, andan application processor (AP) controlling a higher layer, such as anapplication program. According to an embodiment of the disclosure, thecontroller 1 i-40 may include a key updating processor 1 i-42 performinga key updating operation. For example, the controller 1 i-40 may controlthe UE to perform the procedures related to the operation of the UE,illustrated in FIGS. 1D-1H. The controller 1 i-40 and the RF processor 1i-10 and the baseband processor 1 i-20 are not necessarily implementedas separate modules, and may be implemented as one component in the typeof a single chip. The controller 1 i-40 and the RF processor 1 i-10 andthe baseband processor 1 i-20 may be electrically connected. Forexample, the controller 1 i-40 may be a circuit, an application-specificcircuit, or at least one processor. Moreover, operations of the UE maybe implemented by configuring a memory device which stores program codescorresponding to the operations, in a component of the UE.

FIG. 1J is a diagram illustrating a block configuration of a basestation according to an embodiment of the disclosure.

Referring to FIG. 1J, the base station may include a radio frequency(RF) processor 1 j-10, a baseband processor 1 j-20, a backhaulcommunication unit 1 j-30, a storage unit 1 j-40, and a controller 1j-50.

The RF processor 1 j-10 performs a function, such as signal band change,amplification, and the like, for transmitting or receiving a signalthrough a wireless channel. For example, the RF processor 1 j-10 mayupconvert a baseband signal provided from the baseband processor 1 j-20,into an RF band signal, and then transmit the RF band signal through anantenna, and may downconvert an RF band signal received through theantenna, into a baseband signal. For example, the RF processor 1 j-10may include a transmission filter, a reception filter, an amplifier, amixer, an oscillator, a digital-to-analog converter (DAC), ananalog-to-digital converter (ADC), and the like. In FIG. 1J, only oneantenna is illustrated, but the base station may include a plurality ofantennas. In addition, the RF processor 1 j-10 may include a pluralityof RF chains. Moreover, the RF processor 1 j-10 may perform beamforming.To perform the beamforming, the RF processor 1 j-10 may adjust the phaseand size of each of signals transmitted or received through a pluralityof antennas or antenna elements. The RF processor 1 j-10 may perform adownlink MIMO operation by transmitting at least one layer.

The baseband processor 1 j-20 performs a function of conversion betweena baseband signal and a bit stream according to a physical layerprotocol of a system. For example, when data is transmitted, thebaseband processor 1 j-20 generates complex symbols by encoding andmodulating a transmission bit stream. In addition, when data isreceived, the baseband processor 1 j-20 reconstructs a reception bitstream by demodulating and decoding a baseband signal provided from theRF processor 1 j-10. For example, in a case where an orthogonalfrequency division multiplexing (OFDM) scheme is applied, when data istransmitted, the baseband processor 1 j-20 generates complex symbols byencoding and modulating a transmission bit stream, maps the complexsymbols to subcarriers, and then configures OFDM symbols through inversefast Fourier transform (IFFT) calculation and cyclic prefix (CP)insertion. In addition, when data is received, the baseband processor 1j-20 divides a baseband signal provided from the RF processor 1 j-10, bythe units of OFDM symbols, reconstructs signals mapped to subcarriers,through FFT calculation, and then reconstructs a reception bit streamthrough demodulation and decoding. The baseband processor 1 j-20 and theRF processor 1 j-10 transmit and receive a signal as described above.Accordingly, the baseband processor 1 j-20 and the RF processor 1 j-10may be called a transmitter, a receiver, a transceiver, a communicationunit, or a wireless communication unit.

The backhaul communication unit 1 j-30 provides an interface forperforming communication with other nodes within a network.

The storage unit 1 j-40 stores data, such as a basic program, anapplication program, and configuration information for an operation ofthe base station. More particularly, the storage unit 1 j-40 may storeinformation relating to a bearer assigned to a connected UE, ameasurement result reported from a connected UE, and the like. Inaddition, the storage unit 1 j-40 may store information serving as adetermination criterion of whether to provide or stop providingmulti-connection to a UE. The storage unit 1 j-40 provides stored datain response to a request of the controller 1 j-50.

The controller 1 j-50 controls overall operations of the base station.For example, the controller 1 j-50 transmits or receives a signalthrough the baseband processor 1 j-20 and the RF processor 1 j-10, orthrough the backhaul communication unit 1 j-30. In addition, thecontroller 1 j-50 records and reads data in and from the storage unit 1j-40. To this end, the controller 1 j-50 may include at least oneprocessor. The controller 1 j-50 and the RF processor 1 j-10 and thebaseband processor 1 j-20 are not necessarily implemented as separatemodules, and may be implemented as one component in the type of a singlechip. The controller 1 j-50 and the RF processor 1 j-10 and the basebandprocessor 1 j-20 may be electrically connected. For example, thecontroller 1 j-50 may be a circuit, an application-specific circuit, orat least one processor. Moreover, operations of the base station may beimplemented by configuring a memory device which stores program codescorresponding to the operations, in a component of a UE.

Methods disclosed in the claims and/or methods according to variousembodiments described in the specification of the disclosure may beimplemented by hardware, software, or a combination of hardware andsoftware.

When the methods are implemented by software, a computer-readablestorage medium for storing one or more programs (software modules) maybe provided. The one or more programs stored in the computer-readablestorage medium may be configured for execution by one or more processorswithin the electronic device. The at least one program may includeinstructions that cause the electronic device to perform the methodsaccording to various embodiments of the disclosure as defined by theappended claims and/or disclosed herein.

The programs (software modules or software) may be stored innon-volatile memories including a random access memory and a flashmemory, a read only memory (ROM), an electrically erasable programmableread only memory (EEPROM), a magnetic disc storage device, a compactdisc-ROM (CD-ROM), digital versatile discs (DVDs), or other type opticalstorage devices, or a magnetic cassette. Alternatively, any combinationof some or all of them may form a memory in which the program is stored.Further, a plurality of such memories may be included in the electronicdevice.

In addition, the programs may be stored in an attachable storage devicewhich may access the electronic device through communication networks,such as the Internet, Intranet, local area network (LAN), wide LAN(WLAN), and storage area network (SAN) or a combination thereof. Such astorage device may access the electronic device via an external port.Further, a separate storage device on the communication network mayaccess a portable electronic device.

In the above-described detailed embodiments of the disclosure, anelement included in the disclosure is expressed in the singular or theplural according to presented detailed embodiments. However, thesingular form or plural form is selected appropriately to the presentedsituation for the convenience of description, and the disclosure is notlimited by elements expressed in the singular or the plural. Therefore,either an element expressed in the plural may also include a singleelement or an element expressed in the singular may also includemultiple elements.

While the disclosure has been shown and described with reference tovarious embodiments thereof, it will be understood by those skilled inthe art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the disclosure as definedby the appended claims and their equivalents.

What is claimed is:
 1. A method performed by a terminal in a wirelesscommunication system, the method comprising: receiving, from a basestation, a message including information on at least one serving cell;determining whether the message includes a first absolute radiofrequency channel number (ARFCN) for a specific serving cell; anddetermining a first key for a master cell group based on a firstphysical cell identity (PCI) for the specific serving cell and the firstARFCN for the specific serving cell, in case that the message includesthe first ARFCN for the specific serving cell.
 2. The method of claim 1,further comprising: determining the first key for the master cell groupbased on the first PCI for the specific serving cell and a second ARFCNused to determine a current first key for the master cell group, in casethat the message does not include the first ARFCN for the specificserving cell.
 3. The method of claim 1, further comprising: identifyingthat the message includes information for indicating whether the firstPCI and the first ARFCN is used to determine the first key; anddetermining the first key based on a current first key for the mastercell group, in case that the information indicates the first PCI and thefirst ARFCN is not used to determine the first key.
 4. The method ofclaim 3, wherein the determining of whether the message includes thefirst ARFCN for the specific serving cell comprises: determining whetherthe message includes the first ARFCN for the specific serving cell, incase that the information indicates the first PCI and the first ARFCN isused to determine the first key.
 5. The method of claim 1, wherein theinformation on the at least one serving cell comprises the first PCI andtwo ARFCN for the specific serving cell.
 6. The method of claim 5,wherein the first ARFCN among the two ARFCN indicates a center frequencyof a reference signal of the specific serving cell and a second ARFCNindicates a lower end frequency of the specific serving cell.
 7. Themethod of claim 1, wherein the specific serving cell includes a primarycell of the master cell group.
 8. The method of claim 1, wherein thefirst ARFCN for the specific serving cell is listed in the message priorto an ARFCN for other serving cell.
 9. A terminal in a wirelesscommunication system, the terminal comprising: a transceiver; and acontroller configured to: receive, from a base station via thetransceiver, a message including information on at least one servingcell, determine whether the message includes a first absolute radiofrequency channel number (ARFCN) for a specific serving cell, anddetermine a first key for a master cell group based on a first physicalcell identity (PCI) for the specific serving cell and the first ARFCNfor the specific serving cell, in case that the message includes thefirst ARFCN for the specific serving cell.
 10. The terminal of claim 9,wherein the controller is further configured to: determine the first keyfor the master cell group based on the first PCI for the specificserving cell and a second ARFCN used to determine a current first keyfor the master cell group, in case that the message does not include thefirst ARFCN for the specific serving cell.
 11. The terminal of claim 9,wherein the controller is further configured to: identify that themessage includes information for indicating whether the first PCI andthe first ARFCN is used to determine the first key, and determine thefirst key based on a current first key for the master cell group, incase that the information indicates the first PCI and the first ARFCN isnot used to determine the first key.
 12. The terminal of claim 11,wherein the controller is further configured to: determine whether themessage includes the first ARFCN for the specific serving cell, in casethat the information indicates the first PCI and the first ARFCN is usedto determine the first key.
 13. The terminal of claim 9, wherein theinformation on the at least one serving cell comprises the first PCI andtwo ARFCN for the specific serving cell.
 14. The terminal of claim 13,wherein the first ARFCN among the two ARFCN indicates a center frequencyof a reference signal of the specific serving cell and a second ARFCNindicates a lower end frequency of the specific serving cell.
 15. Theterminal of claim 9, wherein the specific serving cell includes aprimary cell of the master cell group.
 16. The terminal of claim 9,wherein the first ARFCN for the specific serving cell is listed in themessage prior to an ARFCN for other serving cell.